User Equipment and Base Station for Mobile Communication System

2. The user equipment of claim 1, wherein the first transmitting time of the source BS is associated with a first time stamp included in one of a first system information block (SIB) and a first unicast radio resource control (RRC) message transmitted by the source BS, and the second transmitting time of the target BS is associated with a second time stamp of one of a second SIB and a second unicast RRC message transmitted by the target BS.

4. The user equipment of claim 3, wherein the uplink grant configuration is carried in one of an RRC message, downlink control information (DCI), and the RRC connection reconfiguration message.

8. The base station of claim 7, wherein the second TA value is carried in one of an RRC message, downlink control information (DCI), and an RRC connection reconfiguration message.

9. The base station of claim 7, wherein the uplink reference signal is one of a demodulation reference signal (DMRS) and a sounding reference signal (SRS).

10. The base station of claim 7, wherein the first reference time is associated with a first local clock of the BS indicated by a first time stamp included in one of a first system information block (SIB) and a first unicast RRC message transmitted by the BS, and the second reference time is associated with a second local clock of the target BS indicated by a second time stamp included in one of a second SIB and a second unicast RRC message transmitted by the target BS.

12. The base station of claim 11, wherein the uplink grant configuration is carried in one of an RRC message, downlink control information (DCI), and the RRC connection reconfiguration message.

15. The base station of claim 14, wherein the second TA value is carried in one of an RRC message, downlink control information (DCI), and an RRC connection reconfiguration message.

16. The base station of claim 14, wherein the uplink reference signal is one of a demodulation reference signal (DMRS) and a sounding reference signal (SRS).

17. The base station of claim 14, wherein the first reference time is associated with a first local clock of the source BS indicated by a first time stamp included in one of a first system information block (SIB) and a first unicast RRC message transmitted by the source BS, and the second reference time is associated with a second local clock of the BS indicated by a second time stamp included in one of a second SIB and a second unicast RRC message transmitted by the BS.

19. The base station of claim 18, wherein the processor further transmits activation downlink control information (DCI) associated with a configured grant identifier to the UE via the transceiver to activate the uplink grant configuration carried in an RRC message.